Glaucoma Clinical Trial
Official title:
Anterior Segment Changes Before and After Uneventful Combined Phaco-Trabeculectomy by Using Optical Coherence Tomography (OCT)
1. Develop a measurement protocol by OCT imaging and characterization of the anterior
chamber change in glaucoma patients before and after surgery.
2. Show the effect of combined surgery in control of intra ocular pressure.
Definitions Glaucoma represents a group of diseases defined by a characteristic optic
neuropathy that is consistent with excavation and undermining of the neural and connective
tissue elements of the optic disc and by the eventual development of distinctive patterns of
visual dysfunction .Pre-perimetric glaucoma is a term that is sometimes used to denote
glaucomatous changes in the optic disc in patients with normal visual fields.
Glaucoma and cataract incidence increases with age. Special considerations are needed when
choosing which surgical strategy to undertake when either of these two conditions requires
surgical management. When performed prior to cataract surgery, trabeculectomy increases the
risk of cataract formation by up to 78%, while subsequent cataract surgery may increase the
risk of elevated intraocular pressure or trabeculectomy failure. By contrast, when cataract
surgery alone is performed in glaucoma patients; an early postoperative intraocular pressure
spike sometimes requiring medical treatment is commonly reported. Therefore,
phacotrabeculectomy, a procedure that combines the management of these two conditions
together in one surgery, may be considered in these situations.
When to Consider Combined Surgery
Combined cataract extraction and glaucoma surgery (trabeculectomy, glaucoma drainage implant
surgery, or any of the newer surgical approaches for glaucoma) should be carefully selected
and individualized depending on clinical findings in each case:
- Cataract surgery alone is sufficient for patients with well controlled in intraocular
pressure in the setting of early to moderate optic nerve damage.
- Patients with uncontrolled intraocular pressure in the presence of severe optic nerve
damage should receive glaucoma surgery first, followed by cataract extraction a few
months later
- Combined surgery may be best suited for a patient with a visually significant cataract
with uncontrolled glaucoma despite maximal medical therapy and/or laser trabeculoplasty.
Cost is often an issue for many patients and eliminating medications can help reduce the
financial burden. Poor compliance with glaucoma medications can also be an issue to
consider both procedures together.
The indication for phaco-trabeculectomy was the simultaneous presence of a visually
significant cataract and open angle glaucoma requiring medications, poor patient compliance,
advanced glaucomatous optic nerve damage or visual field loss, or medically uncontrolled
glaucoma.
Effect of cataract surgery on anterior segment:
Cataract surgery and intraocular lens implantation lead to significant increases in anterior
chamber depth and anterior chamber angle.
Trabeculectomy lead to significant decrease in anterior chamber depth and anterior chamber
angle.The effects of trabeculectomy on anterior segment parameters measured by optical
biometry in Primary open-angle glaucoma and pseudoexfoliation glaucoma and found in primary
open angle glaucoma , intraocular pressure and anterior chamber depth decreased at the 1st
and 3rd months significantly. Conclusion: Trabeculectomy cause some differences in anterior
segment parameters in both primary open angle glaucoma and pseudoexfoliation cases and the
differences between these changes in both groups were found to be insignificant.
Anterior Segment - Optical Coherence Tomography is a useful tool to evaluate filtering blebs
or glaucoma drainage devices in the postoperative period. Clinically , blebs can be described
as diffuse, cystic, encapsulated, or flat. However, these descriptions are subjective and
there may be cases in which clinical appearance does not correlate with bleb function.
Therefore, visualizing intra bleb morphology with anterior segment imaging may enhance our
understanding of different surgical outcomes and wound healing. The noncontact anterior
Segment - Optical Coherence Tomography scanning provides a significant advantage over
ultrasound biomicroscopy in eliminating direct trauma to the bleb or reducing the risk of
potential infection that could occur with the use of an eye-cup or probe .In addition, the
higher scanning resolution of allows differentiating the subconjunctival fluid collection and
the supra sclera fluid space. The anterior segment - optical coherence tomography used to
describe intra- bleb morphology and structures, including bleb wall thickness,
subconjunctival fluid collections, supra sclera fluid space, sclera flap thickness, and
intra-bleb intensity. Anterior segment - optical coherence tomography allows visualization of
the glaucoma drainage devices in the anterior chamber to assess their position or potential
occlusion .
Effect of phacotrabeculectomy on anterior chamber depth:
Phacotrabeculectomy lead to increases in anterior chamber depth and anterior chamber angle.
Poon, Linda Yi-Chieh et al studied comparison of surgical outcomes after phacotrabeculectomy
in primary angle-closure glaucoma versus primary open-angle glaucoma found; the primary angle
closure glaucoma group had an anterior chamber depth that was significantly shallower than
the primary open-angle glaucoma group prior to surgery. However, after surgery, the mean
anterior chamber depth in the primary angle closure glaucoma group increased to a depth
similar to the primary open-angle glaucoma group.
Imaging of the anterior segment of the eye Imaging of the anterior segment of the eye offers
an objective method for visualizing the angle and adjacent anatomical structures. In addition
to qualitative analyses, some imaging modalities permit quantitative analyses that can be
used to monitor change or progression over time.
Ultrasound Biomicroscopy uses high frequency ultrasound (35-100 MHz) to provide high
resolution images of the angle. Ultrasound Biomicroscopy has shown good agreement with
gonioscopy in assessing the anterior chamber angle. Although is a useful technology capable
of providing both qualitative and quantitative analyses, its major advantage lies in its
ability to visualize structures posterior to the iris to detect various causes of secondary
angle closure, such as plateau iris, ciliary effusions, or irido-ciliary masses. The
disadvantages of ultrasound biomicroscopy include required supine position, use of
anesthesia, need for a skilled examiner, longer image acquisition time, and contact with the
eye using a cup with a coupling medium or a probe that can lead to corneal abrasion or
potential infection.
Anterior Segment Optical Coherence Tomography uses the principle of low-coherence
interferometry instead of ultrasound to produce, cross sectional, non-contact,
three-dimensional, high-resolution imaging modality of the anterior segment of the eye. The
technique measures the delay and intensity of the light reflected from the tissue structure
being analyzed and compares it with the light reflected by a reference mirror. The
combination of these two signals results in interference phenomenon. The signal intensity
depends on the optical properties of the tissues, and the device uses these signals to
construct a sagittal cross-section image of the structure being analyzed. OCT technology was
initially used to produce images of the posterior segment of the eye by using a wavelength of
820nm. In 2001, the wavelength was altered to 1310nm to allow better penetration through
light retaining tissues such as the sclera and limbus and to improve visualization of the
anterior segment. Compared with ultrasound biomicroscopy , this technology provides a higher
axial resolution and faster sampling rate (2.0 kHz versus 0.8 kHz). Another main clinical
advantage over ultrasound biomicroscopy is its ability to provide non contact scanning in a
seated, upright position..The major drawback for anterior segment optical coherence
tomography is its inability to visualize structures posterior to the iris due to blockage of
wavelength by pigment. This limits its application in screening several secondary causes of
angle closure, such as plateau iris, ciliary body cyst or tumor, lens subluxation, or ciliary
effusions.
Biometric parameters which can be measured with the anterior segment optical coherence
tomography:
Iris thickness ,iris cross‑ sectional area ,iris curvature ,AC depth ,AC width ,angle opening
distance , angle recess area , scleral thickness, trabecular meshwork ciliary process
distance ,trabecular iris angle , lens vault.
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